| Abstrakt: |
While particulate matter with aerodynamic diameters below 10 and 2.5 mu m (PM[sub 10] and PM[sub 2.5]) correlate with excess mortality and morbidity, there is evidence for still closer epidemiological associations with sulfate ion, and experimental exposure-response studies suggest that the hydrogen ion and ultrafine (PM[sub 0.15]) concentrations may be important risk factors. Also, there are measurement artifacts in current methods used to measure ambient PM[sub 10] and PM[sub 2.5], including negative artifacts because of losses of sampled semivolatile components (ammonium nitrate and some organics) and positive artifacts due to particle-bound water. To study such issues, we are developing a semi-continuous monitoring system for PM[sub 10], PM[sub 2.5], semivolatiles (organic compounds and NH[sub 4]NO[sub 3]), particle-bound water, and other PM[sub 2.5] constituents that may be causal factors. PM[sub 10] is aerodynamically sorted into three size-fractions: (1) coarse (PM[sub 10]-PM[sub 2.5]); (2) accumulation mode (PM[sub 2.5]-PM[sub 0.15]); and (3) ultrafine (PM[sub 0.15]). The mass concentration of each fraction is measured in terms of the linear relation between accumulated mass and pressure drop on polycarbonate pore filters. The PM[sub 0.15] mass, being highly correlated with the ultrafine number concentration, provides a good index of the total number concentration in ambient air. For the accumulation mode (PM[sub 2.5]-PM[sub 0.15]), which contains nearly all of the semivolatiles and particle-bound water by mass, aliquots of the aerosol stream flow into system components that continuously monitor sulfur (by flame photometry), ammonium and nitrate (by chemiluminescence following catalytic transformations to NO), organics (by thermal-optical analysis) and particle-bound water (by electrolytic hygrometer after vacuum evaporation of sampled particles). The concentration of H[sup +] can be calculated (by ion balance using the monitoring data on NO[sub 3][sup -], NH[sub 4][sup +], and SO[sub 4][sup =]). [ABSTRACT FROM AUTHOR] |
